Oil production occurs primarily in offshore fields, from post-salt and pre-salt reservoir rocks, the common characteristic of which is that they are located at great depths below the seabed. This seabed, in turn, is found under water columns that can exceed 3,000 meters in length.
From the reservoir rock to the wellhead, the fluids produced (water, oil, and gas) and the carried sediment travel hundreds or thousands of meters in horizontal, oblique and vertical directions until reaching the Christmas Trees. These fluids and sediments ascend through flexible pipes and rigid pipes called risers from the Christmas Trees to the Stationary Production Units (SPUs).
Environmental conditions outside the subsea well generally involve high pressure and high temperature due to the geothermal gradient that causes a temperature rise of about +1° C. for every 40 meters depth. At the bottom of the sea, in deep waters in Brazil, water temperature is slightly above 0° C.
There is a frequent problem with organic deposits inside various lifting pipe segments, especially in the riser. These deposits are fundamentally complex mixtures of solidified paraffin, resins, asphaltenes and sediments, in addition to all other fluids existing in the well, conditions that may be occluded in the porosities of the deposits. The result of this deposition is the reduction of the useful internal diameter of the pipes and the consequent reduction of the yield of wells and/or Christmas Trees due to flow restrictions and an increase in the loss of load to the surface.
The occurrence of such organic deposits and fouling is a serious problem in well productivity and is usually prevented by adding high cost chemicals such as vinyl acetate copolymers, fatty alcohol polyacrylate and polyphenols to the oil produced, or mechanically prevented, through the preventive use of PIGs. However, in addition to the very high costs, the availability of these products on platforms and the possibility of continuously injecting them represent a great logistical problem at long maritime distances, as well as requiring complex injection operations through peripheral and umbilical pipes, which are not always available.
When it is not possible to prevent organic deposition, a flow restoration is performed. Normally flow restoration is accomplished by injecting a fluid to dissolve the deposit from the SPU, or even by means of mechanical intervention. This restoring fluid, the main function of which is to be a paraffin phase solvent and an asphaltene phase suspender/stabilizer, is injected at high pressure from the SPU to at least the level of the Christmas Tree. It is not uncommon to fill the entire length of the riser and also the production pipe to the deepest section of the well.
The cleaning fluid acts in situ for a period of time, cleaning the inside of the pipes and descaling ancillary equipment such as instruments and valves. After the time of action, the fluid returns to the surface, where it will appropriately come together with most of the deposits responsible for loss of productivity. However, after being used one or more times, said fluid loses its solvent and restorative potential for surfaces, so it is discarded, being disposed of by incorporation into the oil produced.
Among the fluids most used for this cleaning are ketones, kerosene, toluene, xylene, among others. After use, the quantities of this fluid incorporated into the oil are insignificant and will be diluted to infinity at the oil refineries.
Since the interior of the lifting systems includes a volume normally less than 100 m3, the quantity and costs of the fluid represent only a fraction of the benefit of higher productivity of the well, which under optimized conditions yields hundreds or thousands of cubic meters of oil per day. Thus, the criteria of performance, safety, health and availability should be evaluated when choosing the remover fluid.
In terms of performance, light aromatics would be the best choice. However, benzene molecules are known to be carcinogenic and flammable when cold.
Methylbenzene, also known as toluene, is excellent on organic deposits, but this compound has a marked narcotic effect and is also too volatile and flammable when cold.
By increasing the number of carbons of such alkyl benzene to n=8, there are products known as AB-8, in reference to xylene isomers and ethylbenzene. The performance of these products is excellent and their health risks are lower than those of benzene. However, they are volatile and have the appearance of gasoline, as well as being absolutely flammable under deck conditions.
Kerosene, in turn, is a safe product as regards its cold flammability. Its' flash point is established by the ASTM D-56 method at 46° C. It is safer for the users' health and for the environment when compared to aromatics. However, kerosene is generally ineffective in cleaning problematic fouling. On the positive side, it has almost unlimited availability, low cost and is easy.
When working with mixtures, drum logistics must be performed on the deck of the platform as well as risky operations of mixing hazardous fluids aiming to tailor performance to negative externalities such as carcinogenicity, flammability, narcotic effect and cost of component products.
When analyzing the performance of aromatics with a higher number of carbons, such as AB-10 and AB-11, they are not able to adequately dissolve the deposits and fouling. Meanwhile 9-carbon alkyl benzene, sold as mixtures and known under the trade name AB-9, corresponding to the international nomenclature of the Chemical Abstracts Service CAS No. 25551-13-7 and CAS 64742-95-6, offer an excellent compromise between performance, lower cold flammability, risks to health and the environment. These products are certainly suitable and will continue to be used abroad, and also in Brazil, whenever available.
In Brazil, the product that combines the best set of qualities for the proposed removal of deposits, that is, the AB-9—mixture of alkyl benzene with 9 carbons—is very scarce, as it is currently only produced at three petrochemical plants and at one oil refinery. Because it is a product regulated by the National Agency of Oil, Natural Gas and Renewable Fuels (ANP), recipients include fifty authorized consumers who bid for it and who depend on this product for strong economic performance. In this way, Brazilian offshore oil producers do not have access to necessary quantities of AB-9.
Thus, the presented problem reveals the need to find new aromatic based products, with unrestricted availability, deregulated use by the competent authorities, and performance similar to or superior to AB-9.
Numerous attempts at solving the problem of the nature of organic tank-removing fluids in oil production can be found in the prior art. U.S. Pat. No. 4,925,497 reveals a method for removing paraffin and paraffin-like deposits from oil field equipment which involves washing said equipment with a solvent mixture comprising an aromatic hydrocarbon selected from the group consisting of toluene, xylene, mesitylene and mixtures thereof and oil naphtha, the weight ratio of said aromatic hydrocarbon to naphtha being about 10/90 to about 90/10.
Patent SU1326600A1, in turn, proposes the use of a composition for removing deposits of asphalt, resin and wax comprised of 5 to 50% by weight of anisole, 0.1 to 1.0% by weight of polyethylene glycol monoalkyl esters and 49.0 to 94.9% by weight of alkyl aromatic hydrocarbon mixtures consisting of polyalkylbenzene from the production of ethylbenzene or polypropylbenzene from the production of isopropylbenzene.
Patent SU1685967A1 proposes the use of a composition for the removal of asphaltene, resin and paraffin deposits containing 40 to 75% by weight of condensed hydrocarbon and the remainder, a fraction of polyalkyl benzene obtained as a byproduct of the production of isopropylbenzene.
U.S. Pat. No. 4,090,562A describes a method and a composition for stimulating the production of oil in a producing well by the removal of organic deposits. The solvent composition contains 45 to 85% by volume of an aliphatic hydrocarbon, 5 to 45% by volume of benzene, toluene, ethylbenzene, cumene, mesitylene or propylbenzene, 0.56% by volume of ethylene glycol monobutyl ester or monomethyl ester of diethylene glycol and 1 to 15% by volume of methanol, propane, isopropanol or butanol.
Therefore, as shown above, the prior art uses complex mixtures containing aromatic hydrocarbons for removal of organic deposits and fouling.
None of the prior art documents describe a simple, easily obtainable composition to remove organic deposits and fouling, with a simple to obtain high performance aromatic base resulting in faster, economical and safer removal.
As will be better described below, the present invention seeks to resolve the above-described problems of the prior art in a practical and efficient manner.